This invention relates to multistage fluid pressure actuators, and more particularly the invention is concerned with an actuator of the class described in which a rotational movement takes place at the first stage.
In industrial robots and machine tools, a structural arrangement in which a first member supports a second member for movement and the second member in turn supports a third member for movement has hitherto had many applications. In this structural arrangement, a first drive means for driving the second member is fixedly secured to the first member and a second drive means for driving the third member is fixedly secured to the second member in many applications. With regard to a method for supplying fluid power to the first and second drive means, no difficulty is encountered in supplying fluid power to the first drive means if the first member is a base, for example, which is fixed in place, because the first drive means does not move. However, it is not easy to transmit fluid power to the second drive means because the second member to which the second drive means is fixedly secured undergoes some sort of movement.
In many cases, flexible pipes have hitherto been used for transmitting fluid power to drive means subjected to movement. When pipes are used for this purpose, it is necessary to select for them positions in which they are arranged in such a manner that their pressure does not interfere with the operation of the apparatus. Selection of such positions raises a problem which is hard to solve from the point of view of design. Moreover, since repeated stress is applied to the pipes, the pipes tend to be damaged, thereby making it necessary to perform inspection often to keep them in good working conditions.
The fluid pressure actuators disclosed in Japanese Patent Laid-open Publication No. 12081/76, Japanese Patent Laid-open Publication No. 111578/76 and Japanese Utility Model Laid-open Publication No. 117787/77 are constructed such that a fluid is supplied through passages formed in a first member and a second member to the second member and a third member for moving the same, thereby dispensing with piping located outside the actuators. Generally, fluid pressure actuators including those of the prior art described hereinabove have a large number of parts which require precise machine finishes in production.